Process for removing flyslag from gas

ABSTRACT

A process for the treatment of flyslag from the gasification of coal is described, the process being characterized, in one embodiment, by mixing of the flyslag with a cementitious material, a composition capable of converting sulfides in the flyslag at least to sulfur, and an aqueous waste stream from the gasification of coal, in specified proportions. A composition comprising flyslag, a cementitious material, and a composition capable of converting sulfides in the flyslag at least to sulfur, is also disclosed.

BACKGROUND OF THE INVENTION

Partial combustion or gasification of coal involves reacting the coal atelevated temperatures and possibly elevated pressures with a limitedvolume of oxygen, the reaction preferably being carried out in thepresence of additional agents such as steam, carbon dioxide, or variousother materials. Gasification of coal produces a gas, known as synthesisgas, that contains mostly carbon monoxide and hydrogen. Also producedare varying quantities of other gases, such as carbon dioxide andmethane, and various liquid and solid materials, such as small particlesof ash and carbon commonly known and collectively defined herein asflyslag or flyash. This flyslag, because it is derived from a "reducing"atmosphere, tends to be different in composition and properties fromflyash normally associated with combustion boilers where a fullyoxidizing atmosphere is utilized. For example, the flyslag fromprocesses for partial combustion of coal may contain elemental iron,sulfides, and deposited carbon, components not normally associated withboiler flyash. In general, the flyslag or flyash entrained with the gasin partial combustion processes is usually removed from the rawsynthesis gas by a combination of cyclones or separators, or a waterscrubbing system employing washer coolers, venturi scrubbers, or filtersor electrostatic precipitators, or combinations of these systems.

The raw synthesis gas from the gasifier or gasification zone contains,in addition to the aforementioned materials, sulfur-containing gases,such as hydrogen sulfide and carbonyl sulfide, as well as small amountsof ammonia and hydrogen cyanide. The presence of HCN, NH₃, and COS insynthesis gas derived from the gasification of coal complicates removalof additional impurities such as H₂ Sand/or CO₂, and poses problemsinsofar as product quality and pollution control requirements areconcerned. Although HCN, NH₃, and COS are present, as indicated, inquite minor quantities, for example, normally less than 1 percent byvolume, combined, of the total raw synthesis gas stream, they must bedealt with before the synthesis gas is utilized.

The flyslag or flyash removed from the synthesis gas may haveundesirable properties insofar as its ultimate disposal is concerned.For example, it may be light, friable, dusty and difficult to compact.Because it may contain unsuitable species such as arsenic, selenium, andsulfides, it must be handled with care, and, if it is to be utilized ordisposed of as land fill, must be in a form which does not release suchmaterials readily to the environment. The sulfides present areparticularly troublesome since, upon contact with strongly acidicmaterial, hydrogen sulfide will be evolved. The invention addresses theproblems of flyslag treatment, concomitantly accomplishing the treatmentand utilization of other nominal waste products from the gasificationprocess.

SUMMARY OF THE INVENTION

Accordingly, in one embodiment, the invention relates to a process forremoving flyslag from a synthesis gas stream from which the bulk of theflyslag has already been removed comprising

(a) passing said gas stream to a scrubbing zone which includes orcomprises a loaded scrubbing solution stripping section, and scrubbingsaid gas stream with an effective amount of an aqueous scrubbingsolution, and removing remaining flyslag particles and HCN, NH₃, and COSfrom said gas stream, producing a partially purified gas streamsubstantially free of flyslag, and an aqueous stream containing flyslagparticles from said stripping section, and passing said aqueous streamto a concentrating zone;

(b) removing from said concentrating zone a concentrated aqueous streamderived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone;

(c) mixing a major portion of flyslag and a minor portion ofcementitious material and an effective amount of a composition capableof converting sulfides in said flyslag at least to sulfur, with at leasta portion of the concentrated aqueous stream from step (b), theconcentrated aqueous stream being supplied in a ratio of from about onepart to about five parts concentrated aqueous stream per part, byweight, combined total solids of flyslag and cementitious material, andproducing a solid flyslag composite having improved disposal properties.

In another embodiment, the invention relates to a process in which a gasstream containing flyslag, derived from the gasification of coal, istreated by

(a) passing said gas stream containing flyslag to a solids separationzone, and separating the bulk of the flyslag in said zone, producingsolid flyslag and a gas stream having reduced flyslag content;

(b) passing gas stream having reduced flyslag content from step (a) to ascrubbing zone which includes a loaded scrubbing solution strippingsection, and scrubbing said gas stream with an effective amount of anaqueous scrubbing solution, and removing HCN, NH₃, and COS and remainingflyslag particles from said gas stream, producing a partially purifiedgas stream substantially free of flyslag, and an aqueous streamcontaining flyslag particles from said stripping section, and passingsaid aqueous stream to a concentrating zone;

(c) removing from said concentrating zone a concentrated aqueous streamderived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone;

(d) mixing a major portion of flyslag from step (a), a minor portion ofcementitious material, and an effective amount of a composition capableof converting sulfides in said flyslag at least to sulfur, with at leasta portion of the concentrated stream from step (c), the concentratedaqueous stream being supplied in a ratio of from about one part to aboutfive parts concentrated aqueous stream per part, by weight, combinedtotal solids of flyslag and cementitious material; and producing a solidflyslag composite having improved disposal properties.

In yet another embodiment, the invention relates to a process for thegasification of coal comprising

(a) partially combusting particulate coal in a gasification zonecomprising at least one gasification reactor, and producing a hotgaseous stream containing synthesis gas, flyslag, and minor amounts ofHCN, NH₃, and COS;

(b) quenching and cooling said hot gaseous stream, and removing at leastthe bulk of the flyslag therefrom, producing a cool gaseous streamhaving reduced flyslag content;

(c) passing cool gas stream having reduced flyslag content from step (b)to a scrubbing zone which includes a loaded scrubbing solution strippingsection and scrubbing said gaseous stream with an effective amount of anaqueous scrubbing solution, and removing HCN, NH₃, and COS and remainingflyslag particles from said gas stream, producing a partially purifiedgas stream substantially free of flyslag, and an aqueous streamcontaining flyslag particles from said stripping section, and passingsaid aqueous stream to a concentrating zone;

(d) removing from said concentrating zone a concentrated aqueous streamderived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone;

(e) mixing a major portion of flyslag derived from at least onegasification reactor of step (a), a minor portion of cementitiousmaterial, and an effective amount of a composition capable of convertingsulfides in said flyslag at least to sulfur, with at least a portion ofthe concentrated stream from step (d), the concentrated aqueous streambeing supplied in a ratio of from about one part to about five partsconcentrated aqueous stream per part, by weight, combined total solidsof flyslag and cementitious material, and producing a solid flyslagcomposite having improved disposal properties.

In a separate embodiment, the invention relates to a readily disposableflyslag composite formed by mixing a major portion of flyslag, a minorportion of cementitious material, an effective amount of a compositioncapable of converting sulfides in said flyslag at least to sulfur, andwater, the water being present in a ratio of from about one part toabout five parts water per part, by weight, combined total solids offlyslag and cementitious material. Preferably, the composition capableof converting sulfides is present in a ratio of at least one equivalentof said composition per equivalent of sulfur in the flyslag, and thewater is present in an amount of from one and one half parts to threeparts, per part, by weight, combined total solids of flyslag andcementitious material. Preferably, the flyslag composite may be formedby mixing the flyslag and water, then adding the cementitious materialand the composition capable of converting sulfides, in the proportionsmentioned. The water, the composition capable of converting sulfides,and the cementitious material may also be mixed, and then the flyslagadded, in the proportions mentioned, but this is not preferred. As usedherein, the term "cementitious material" refers to compositionscomprising alumina, silica, lime, iron oxide and magnesia burnedtogether in a kiln and finely pulverized, which when mixed with water toform a plastic mass, hardens by chemical combination and by gelation andcrystallization. Suitable examples of such material include, but are notlimited to, portland cement, alumina cement, and natural cement. Theterm "water" is generally taken to mean any source of water, includingpure water and "impure" water from a variety of sources, and thus willinclude water containing impurities, both liquid, solid, and gaseous.For example, the water employed may be a concentrated waste slurrystream, as described herein, and may include, but is not limited to,effluent streams, waste streams, blowdown, etc. Those skilled in the artwill recognize that the only significant limitation is that theconcentrations or character of any extraneous components of the "water"do not interfere to any substantial extent with the aggregation orformation of the composites or desired properties of such compositesdescribed herein, or do not pose significant environmental problemsthemselves. The term "composition capable of converting sulfides in saidflyslag at least to sulfur" or variations thereof used herein refers tothose compositions or compounds, or mixtures thereof, which possesssufficient oxidative capacity to convert sulfur present as sulfides inthe flyslag to elemental sulfur (zero valence) or to a higher oxidizedstate, such as in a sulfate. It thus excludes compositions, such asstrong acids, which would generate H₂ S, and obviously, sulfides. Whilethose skilled in the art may select suitable oxidants, acceptablereactants include alkali and alkaline earth persulfates andperchlorates; iron (III) salts, such as the chloride, bromide, andnitrate; alkali and alkaline earth ferrates; peroxides, such as hydrogenperoxide, and chromates and permanganates. As noted, an effective amountof the composition capable of converting sulfides in the flyslag atleast to sulfur is employed, i.e., an amount sufficient to convert atleast the bulk of the sulfides present at least to sulfur. This amount,per given mass of flyslag, may be determined by analysis of the sulfidecontent of the flyslag. Preferably, sufficient composition to convert,preferably on at least a stoichiometric basis, the sulfides is employed,and normally, an excess of the composition will be employed.

DETAILED DESCRIPTION OF THE INVENTION

The partial combustion of coal to produce synthesis gas, which isessentially carbon monoxide and hydrogen, and particulate flyslag, iswell known, and a survey of known processes is given in "UllmannsEnzyklopadie Der Technischen Chemie", vol. 10 (1958), pp. 360-458.Several such processes for the preparation of hydrogen and carbonmonoxide, flyslag-containing gases are currently being developed.Accordingly, details of the gasification process are related onlyinsofar is as necessary for understanding of the present invention.

In general, the gasification is carried out by partially combusting thecoal with a limited volume of oxygen at a temperature normally between800° C. and 2000° C., and preferably at a temperature between 1050° C.and 2000° C. If a temperature of between 1050° C. and 2000° C. isemployed, the product gas may contain very small amounts of gaseous sideproducts such as tars, phenols and condensable hydrocarbons. Suitablecoals include lignite, bituminous coal, sub-bituminous coal anthracitecoal, and brown coal. Lignites and bituminous coals are preferred. Inorder to achieve a more rapid and complete gasification, initialpulverization of the coal is preferred. Particle size is preferablyselected so that 70% of the solid coal feed can pass a 200 mesh sieve.The gasification is preferably carried out in the presence of oxygen andsteam, the purity of the oxygen preferably being at least 90% by volume,nitrogen, carbon dioxide and argon being permissible as impurities. Ifthe water content of the coal is too high, the coal should be driedbefore use. The atmosphere will be maintained reducing by the regulationof the weight ratio of the oxygen to moisture and ash free coal in therange of 0.6 to 1.0, preferably 0.8 to 0.9. The specific details of theequipment and procedures employed form no part of the invention, butthose described in U.S. Pat. Nos. 4,350,103 and 4,458,607, bothincorporated herein by reference, may be employed. Although, in general,it is preferred that the ratio between oxygen and steam be selected sothat from 0.1 to 1.0 parts by volume of steam is present per part byvolume of oxygen, the invention is applicable to processes havingsubstantially different ratios of oxygen to steam. The oxygen used ispreferably heated before being contacted with the coal, preferably to atemperature of from about 200° to about 500° C.

The details of the gasification reactor system form no part of thepresent invention, and suitable reactors are described in British Pat.No. 1501284 and U.S. Pat. No. 4,022,591. The high temperature at whichthe gasification is carried out is obtained by reacting the coal withoxygen and steam in a reactor at high velocity. A preferred linearvelocity is from 10 to 100 meters per second, although higher or lowervelocities may be employed. The pressure at which the gasification canbe effected may vary between wide limits, preferably being from 1 to 200bar. Residence times may vary widely; common residence times of from 0.2to 20 seconds are described, with residence times of from 0.5 to 15seconds being preferred.

After the starting materials have been converted, the reaction product,which comprises hydrogen, carbon monoxide, carbon dioxide, and water, aswell as the aforementioned impurities, is removed from the reactor. Thisgas, which normally has a temperature between 1050° C. and 1800° C.,contains the impurities mentioned and flyash, includingcarbon-containing solids. In order to permit removal of these materialsand impurities from the gas, the reaction product stream should first bequenched and cooled. A variety of elaborate techniques have beendeveloped for cooling the gaseous stream, the techniques in generalbeing characterized by use of a quench gas and boiler in which steam isgenerated with the aid of the waste heat. Cyclones or other suitabletechniques may be provided for removing particulate solids from thegaseous stream. Even though such procedures may be practiced, furtherreduction of the solids content may nevertheless be desirable. To thisend, the gas stream is preferably passed through a scrubbing zone, whereit is washed with an aqueous scrubbing solution. The scrubbing zone maycomprise one or more scrubbing sections or "scrubbers". The term"aqueous scrubbing solution", as used herein, includes, but is notlimited to, water, various process streams, and solution from which theHCN, NH₃ and COS have been stripped, i.e., recycle, as well as solutiontreated by hydrolysis, as further hereinafter described. As used herein,the term "loaded" merely indicates that the scrubbing solution orsolutions, after scrubbing the gaseous stream, contain finite quantitiesof one or more of the impurity gases mentioned and particulate flyslagsolids. The aqueous scrubbing solution may contain materials, such asselective amines, to assist in impurity removal, and caustic may beadded to adjust pH and optimize removal. Water is effective for HNN andNH₃, and amine solution may be added for COS removal, in a separatestage, if desired. If more than one stage is employed, the solutions mayor may not be combined before their entry into the stripping zone. Theaqueous scrubbing solution may also contain ammonium polysulfide, whichreacts with the HCN in the gas stream to form ammonium thiocyanate.Depending on the type of scrubbing solution employed, differenttreatment of "spent" or "loaded" solution will be required. For example,if water (and recycle water) is used as the aqueous scrubbing solution,the loaded solution may be forwarded to a stripping section where theHCN and NH₃ may be stripped and sent for disposal. If ammoniumpolysulfide is employed in the aqueous scrubbing solution, the spentthiocyanate containing solution is sent to a hydrolysis zone where thethiocyanate is hydrolyzed to produce NH₃, CO₂, and H₂ S. In this casethe solution may then be stripped in a stripping section, and thereleased gases are processed as desired. Suitable hydrolysis techniquesare described in U.S. Pat. Nos. 4,497,784, 4,505,881, and 4,508,693, allto Diaz, incorporated herein by reference. What is required in severalembodiments of the invention, however, is that the scrubbing zonecomprise or include such a stripping section, a bleed or aqueous streamfrom the stripping section being employed to regulate concentration offlyslag particulates and impurities in the scrubbing zone. The aqueousstream or bleed size is not critical, but will preferably comprise fromabout 33 percent to 100 percent by volume of the aqueous stream orsolution entering the section. Those skilled in the art may adjust thepH, composition, and volumes of aqueous scrubbing solution to supply anamount effective to remove substantially all, if not all, of the HCN,NH₃, COS, and flyslag from the synthesis gas stream. Suitable scrubbingapparatus has been described in U.K. Pat. No. 826,209. As a result ofsuch a washing treatment, a gas is obtained which contains hardly anysolids, and which preferably has a temperature between 20° C. and 40° C.

As indicated, the invention includes the treatment of the contaminatedor "loaded" scrubbing solution, with the aim of utilizing a portionthereof in an efficient manner. In one case, aqueous scrubbing solutioncontaining dissolved HCN, NH₃ and COS, is fed to a stripping zone orstripper where the impurity gases are stripped from the solution. Thisprocedure is accomplished preferably by forwarding solution from thescrubbing zone as a bleed stream therefrom, to a stripping zone whereinsuitable techniques are employed to strip the impurity gases from thesolution. The treatment of the hydrolysis zone effluent, in the case ofpolysulfide addition, has been noted, supra.

In the stripper, the scrubbing solution may be stripped by heating,contact with a nonreactive gas, or a combination of heating and gas flowstripping. The stripping produces, in one case, a gas stream containingHCN, NH₃, and COS, in the polysulfide case, NH₃, CO₂, and H₂ S. Thestripped solution, as indicated, contains particulate flyslag solids orfines, these fines being present from infinitesimal amounts to amountsof from about 2% by weight to about 5% by weight. This fines contentdetermines the treatment of the solution described herein. Preferably,the bulk of the stripped solution is returned to the scrubbing zone forreuse. Caustic may be added in the stripper to assist release of NH₃.

Whatever the case, as indicated, the scrubbing solution may be strippedby heating, or by use of flow of a non-reactive gas (or both). If heatalone is applied to the scrubbing solution, sufficient heat will besupplied to release the dissolved gases. Generally, temperatures on theorder of about 80° C. to about 150° C., preferably from about 80° C. toabout 120° C., will be sufficient to release the dissolved gases.

If a non-reactive stripping gas is employed, it will be supplied at asuitable pressure, for example 3 to 5 atmospheres, to strip thedissolved gases from the scrubbing solution. Any suitable strippingdevice may be used, such as packed column or a tray column. Differentdevices may be used (whether stripping is accomplished by heat, gasflow, or a combination thereof) where plugging by solids may be aproblem. In any event, any suitable non-reactive gas may be employed. Asused herein, the term "non-reactive" implies that the gas does not reactwith the scrubbing solution to any substantial extent. Suitable gases,under the conditions in the stripping zone, include air, steam, carbondioxide, oxygen, nitrogen, and inert gases. Steam is much preferred,since it can provide heat for the stripping and may be condensed easily,leaving a relatively concentrated stream. Those skilled in the art mayadjust volumes and velocities of the stripping gas to appropriatelevels. As indicated, heat may be supplied in the case of a strippinggas to assist the stripping.

The stripped impurity gases are separated and removed from the scrubbingsolution and, depending on their nature, for example, may be forwardedto a gasification reactor. If a multiplicity of gasification reactors isemployed in the gasification zone, the impurity gases from the strippingzone may be sent to any one or all of the reactors, as desired orappropriate. If the gasification reactor is operated under highpressure, as is commonly the case, the pressure of the impurity gasstream must be increased for entry of the gases into the reactor.Suitable devices for doing so are within the skill of the art, and assuch, form no part of the present invention. Alternately, the strippedgases may be sent for chemical treatment or recovery.

In accordance with the invention, a minor portion or bleed stream of thestripped solution is removed from the stripping zone, and is sent to aconcentrating zone. In such zone, the minor portion or bleed stream maybe treated in one or more ways to produce a concentrated aqueous streamhaving a ratio of particulate flyslag or flyash solids to liquid greaterthan that of the portion or bleed entering the concentrating zone. Thus,the portion or bleed (or a portion thereof) may be clarified or settled,or may be filtered, or subjected to any suitable combination of suchtreatments to produce the concentrated aqueous stream. Preferably, themixture is first sent clarified, and the underflow is sent to, e.g.,static filters or thickeners. Preferably, the concentrated aqueousstream removed from the thickeners or filters will have a particulateflyslag or fines content of from five or ten percent by weight to twentyto thirty percent by weight, most preferably ten percent to twentypercent by weight, based on the weight of the stream and flyslag. Thoseskilled in the art will recognize that the concentrated aqueous streamalso contains minor amounts, e.g., 0.1 to 0.5 percent by weight, ofresidual impurities such as chlorides and sulfates. Clarified orfiltered liquid from the concentrating zone may be utilized in theprocess again, if desired, or may be sent to treatment.

The concentrated aqueous stream is forwarded to a mixing zone, where itis combined, as hereinafter described, with flyslag. The source of theflyslag is not critical, but, of course, the most usual source will bethe flyslag produced in a previous step of the process, or in anassociated gasification process scheme if a gasification zone having amultiplicity of reactors is utilized. The flyslag may also be that fromwhich residual carbon values have been removed, as for example, byoxidation of "ordinary" flyslag, or as described in copendingapplication Ser. No. 813,737, entitled Flyash Process, by Hardesty,filed Dec. 27, 1985, and now abandoned, incorporated herein byreference. Again, the flyslag, oxidant composition, and cementitiousmaterial may be mixed with any appropriate aqueous stream available,water being suitable. The use of the concentrated aqueous streamaccomplishes the disposal of remaining fines from the concentratingzone, at the same time disposing of some liquid effluent. If the volumeof the concentrated aqueous stream is insufficient to produce the typeof product desired, water from any other source may be added.

Any suitable mixing device or devices, such as a pug mill, may beutilized for the mixing. As indicated, the flyslag, the oxidantcomposition, the cementitious material, and the water will be mixed inthe proportions mentioned to provide a mixture having the desiredcharacteristics. Most preferably, the flyslag and cementitious materialwill be mixed in a ratio of from about 0.05 part to about 0.3 partcementitious material per part flyslag, by weight, water being appliedin a ratio of from about one part to about five parts water per part, byweight, combined total solids of flyslag and cementitious material.Pressures in the concentrating and mixing zone are not critical and maybe atmospheric or greater. Temperatures in the concentration and mixingzone are similarly not critical, and may range from atmospheric to 150°C. or more. The conditions and proportions described will normallyproduce a solid mixture having reduced dusting tendencies, and whichmixture is easily transported or disposed.

In order to illustrate the invention more fully, reference is made tothe accompanying schematic drawing. The drawing is of the process flowtype in which auxillary equipment, such as valves, pumps, etc., havebeen omitted therefrom. All valves are merely exemplary or calculated.

Accordingly, pulverulent coal is passed via line (1) into a coal dryer(2) where the coal is dried, suitably at a temperature of about 200° C.The dry coal is subsequently discharged through a line (3) and passedinto a gasification reactor (4) where it is gasified at a temperature ofabout 1500° C. to about 2000° C., a pressure of about 35 atmospheresabsolute, with oxygen, which is supplied through a line (5). Thegasification produces a product or synthesis gas which is removed fromthe upper portion (6) of the reactor, and a slag which is removed fromthe lower portion of the reactor via line (7). The gasification productis removed via conduit (8) where it is quenched and then passed througha boiler or heat exchange zone (9) where it is cooled to a temperatureof about 200° C. In the heat exchange zone (9), water which is suppliedthrough line (10) is converted by indirect heat exchange to highpressure steam, the steam being discharged through a line (11). Thecooled gasification product is passed through a line (12) to a series ofcyclones (13) where the bulk of the particulates (flyslag) is removedand sent via line (14) to storage in vessel (15). The synthesis gas thenpasses via line (16) to scrubber (17) where it is contacted with anaqueous scrubbing solution. Water and/or recycle scrubbing watersolution are supplied to scrubber (17) through line (18). In scrubber(17) a scrubbing solution containing ammonium polysulfide converts HCNand absorbs ammonia and COS present in the gaseous stream, and removessoot and remaining flyslag therefrom. Purified synthesis gas passes fromscrubber (17) through line (19) on to further treatment and/or recovery.Scrubbing water, containing dissolved gases, ammonium thiocyanate, andflyslag and soot, is removed from the lower portion of scrubber (17) andis sent by line (20) to a hydrolysis zone (21). Internal recycle forscrubber (17) is provided by line (18). Hydrolysis zone (21) comprisesmerely a holding vessel maintained at about 250° C., and an averageresidence time for a given portion of solution will be from 30 minutesto one hour. Water is supplied if needed, and the ammonium thiocyanatein the mixture hydrolyzes to NH₃, CO₂, and H₂ S. The gas-liquid mixtureis forwarded via line (22) to stripping zone or column (23) where thegases are stripped from solution. Stripping zone (23) comprises astripper contactor of the tray type, in which liquid is introduced intothe top of the column and a non-reactive gas is introduced via line (24)into the bottom of the column. Preferably, steam, at a temperature of300° F., is employed in stripping the gases, so that upon leaving column(23), through line (25), the now freed impurity gases and the steam inline (25) are suitably conveyed for chemical and/or biologicaltreatment. Solution containing ammonium polysulfide is removed via line(26) and returned, with suitable make-up, if necessary, for use inscrubber (17). If water is the aqueous scrubbing liquid, hydrolysis zone(21) may be omitted, HCN, NH₃ and COS being removed from scrubber (23)via line (25). From stripper (23), a bleed stream (27), which willcomprise from about 33 percent to about 100 percent, preferably about 40percent to 60 percent, by volume, of the total flow in line (22) tocolumn (23), and containing about 3 percent by weight of flyslag andunreacted solids, is continuously removed and sent to a concentratingzone (28). Concentrating zone (28) comprises a clarifier vessel fromwhich a clarified liquid is removed overhead via line (29) for chemicaland/or biological treatment. A bottom stream containing about 15 percentby weight of flyslag and unreacted solids is removed via line (30), andis sent to a pug mill (31). In pug mill (31) flyslag from vessel (15),sent via line (32), is combined with the bottom stream and with portlandcement and sodium persulfate, the concentrated bottom stream beingcombined with the flyslag and cement in a ratio of about 1.5 partsconcentrated clarifier bottoms to one part flyslag, 0.1 part portlandcement, and at least one equivalent of the persulfate. A pasty flyslag,composite is removed for utilization or disposal at the exit of the pugmill.

While the invention has been illustrated with particular apparatus,those skilled in the art will appreciate that, except where specified,other equivalent or analogous units may be employed. The term "zone", asemployed in the specification and claims, includes, where suitable, theuse of segmented equipment operated in series, or the division of oneunit into multiple units to improve efficiency or overcome sizeconstraints, etc. For example, a series of scrubbers might be employed,with different aqueous solutions, at least the bulk of the "loaded"solutions being sent to one or more strippers. Parallel operation ofunits, is, of course, well within the scope of the invention. Asdescribed, of course, if water is the scrubbing solution, the hydrolysiszone is omitted and provision is made for HCN, etc. treatment.

What is claimed is:
 1. A process for removing flyslag from a synthesisgas stream from which the bulk of the flyslag has already been removedcomprising(a) passing said gas stream to a scrubbing zone which includesa loaded scrubbing solution stripping section, and scrubbing said gasstream with an effective amount of an aqueous scrubbing solution, andremoving remaining flyslag particles and HCN, NH₃, and COS from said gasstream, producing a partially purified gas stream substantially free offlyslag, and an aqueous stream containing flyslag particles from saidstripping section, and passing said aqueous stream to a concentratingzone; (b) removing from said concentrating zone a concentrated aqueousstream derived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone; (c) mixing a major portion of flyslaghaving sulfides present therein, a minor portion of cementitiousmaterial and an effective amount of a composition capable of convertingsulfides in said flyslag at least to sulfur, with at least a portion ofthe concentrated aqueous stream from step (b), the concentrated aqueousstream being supplied in a ratio of from about one part to about fiveparts concentrated aqueous stream per part, by weight, combined totalsolids of flyslag and cementitious material, and producing a solidflyslag composite having improved disposal properties.
 2. A process forthe removal of flyslag from a gas stream containing flyslag, the flyslaghaving sulfides present therein and the gas stream derived from thegasification of coal, comprising(a) passing said gas stream containingsaid flyslag to a solids separation zone, and separating the bulk of theflyslag in said zone, producing solid flyslag and a gas stream havingreduced flyslag content; (b) passing gas stream having reduced flyslagcontent from step (a) to a scrubbing zone which includes a loadedscrubbing solution stripping section, and scrubbing said gas stream withan effective amount of an aqueous scrubbing solution, and removing HCN,NH₃, and COS and remaining flyslag particles from said gas stream,producing a partially purified gas stream substantially free of flyslag,and an aqueous stream containing flyslag particles from said strippingsection, and passing said aqueous stream to a concentrating zone; (c)removing from said concentrating zone a concentrated aqueous streamderived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone; (d) mixing a major portion of flyslagfrom step (a) and a minor portion of cementitious material and aneffective amount of a composition capable of converting sulfides in saidflyslag at least to sulfur, with at least a portion of the concentratedstream from step (c), the concentrated aqueous stream being supplied ina ratio of from about one part to about five parts concentrated aqueousstream per part, by weight, combined total solids of flyslag andcementitious material; and producing a solid flyslag composite havingimproved disposal properties.
 3. A process for the gasification of coalcomprising(a) partially combusting particulate coal in a gasificationzone comprising at least one gasification reactor, and producing a hotgaseous stream containing synthesis gas, flyslag having sulfides presenttherein, and minor amounts of HCN, NH₃, and COS; (b) quenching andcooling said hot gaseous stream, and removing at least the bulk of theflyslag therefrom, producing a cooled gaseous stream having reducedflyslag content; (c) passing cool gas stream having reduced flyslagcontent from step (b) to a scrubbing zone which includes a loadedscrubbing solution stripping section, and scrubbing said gaseous streamwith an effective amount of an aqueous scrubbing solution, and removingHCN, NH₃, and COS and remaining flyslag particles from said gas stream,producing a partially purified gas stream substantially free of flyslag,and an aqueous stream containing flyslag particles from said strippingsection, and passing said aqueous stream to a concentrating zone; (d)removing from said concentrating zone a concentrated aqueous streamderived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone; (e) mixing a major portion of saidflyslag derived from at least one gasification reactor of step (a) and aminor portion of cementitious material and an effective amount of acomposition capable of converting sulfides in said flyslag at least tosulfur, with at least a portion of the concentrated stream from step(d), the concentrated aqueous stream being supplied in a ratio of fromabout one part to about five parts concentrated aqueous stream per part,by weight, combined total solids of flyslag and cementitious material,and producing a solid flyslag composite having improved disposalproperties.
 4. A process for removing flyslag from a synthesis gasstream from which the bulk of the flyslag has already been removedcomprising(a) passing said gas stream to a scrubbing zone, and scrubbingsaid gas stream with an effective amount of an aqueous scrubbing liquid,and removing remaining flyslag particles and HCN, NH₃, and COS from saidgas stream, producing a partially purified gas stream substantially freeof flyslag and a loaded aqueous scrubbing solution; (b) stripping thebulk of the HCN, NH₃, and COS from at least a portion of said loadedsolution in a stripping zone; (c) removing an aqueous stream containingflyslag particles from said stripping zone, and passing said aqueousstream to a concentrating zone; (d) removing from said concentratingzone a concentrated aqueous stream derived from said aqueous stream andhaving a ratio of flyslag particulate solids to liquid greater than thatof the aqueous stream entering said concentrating zone; (e) mixing amajor portion of flyslag having sulfides present therein and a minorportion of cementitious material and an effective amount of acomposition capable of converting sulfides in said flyslag at least tosulfur, with at least a portion of the concentrated aqueous stream fromstep (d), the concentrated aqueous stream being supplied in a ratio offrom about one part to about five parts concentrated aqueous stream perpart, by weight, combined total solids of flyslag and cementitiousmaterial, and producing a solid flyslag composite having improveddisposal properties.
 5. A process for the removal of flyslag from a gasstream containing flyslag, the flyslag having sulfides present thereinand the gas stream derived from the gasification of coal, comprising(a)passing said gas stream containing said flyslag to a solids separationzone, and separating the bulk of the flyslag in said zone, producingsolid flyslag and a gas stream having reduced flyslag content; (b)passing gas stream having reduced flyslag content from step a) to ascrubbing zone, and scrubbing said gas stream with an effective amountof an aqueous scrubbing liquid, and removing HCN, NH₃, and COS andremaining flyslag particles from said gas stream, producing a partiallypurified gas stream substantially free of flyslag and a loaded aqueousscrubbing solution; (c) stripping the bulk of the HCN, NH₃, and COS fromat least a portion of said loaded scrubbing solution in a strippingzone; (d) removing an aqueous stream containing flyslag particles fromsaid stripping zone, and passing said aqueous stream to a concentratingzone; (e) removing from said concentrating zone a concentrated aqueousstream derived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone; (f) mixing a major portion of flyslagfrom step (a), and a minor portion of cementitious material and aneffective amount of a composition capable of converting sulfides in saidflyslag at least to sulfur, with at least a portion of the concentratedstream from step (e), the concentrated aqueous stream being supplied ina ratio of from about one part to about five parts concentrated aqueousstream per part combined total solids of flyslag and cementitiousmaterial, and producing a solid flyslag composite having improveddisposal properties.
 6. A process for the gasification of coalcomprising(a) partially combusting particulate coal in a gasificationzone comprising at least one gasification reactor, and producing a hotgaseous stream containing synthesis gas, flyslag having sulfides presenttherein and minor amounts of HCN, NH₃, and COS; (b) cooling said gaseousstream, and removing at least the bulk of the flyslag therefrom,producing a cooled gaseous stream having reduced flyslag content; (c)passing cool gas stream having reduced flyslag content from step (b) toa scrubbing zone, and scrubbing said gaseous stream with an effectiveamount of an aqueous scrubbing liquid, and removing HCN, NH₃ and COS andremaining flyslag particles from said gas stream, producing a partiallypurified gas stream substantially free of flyslag and a loaded aqueousscrubbing solution; (d) stripping the bulk of the HCN, NH₃ and COS fromat least a portion of said loaded scrubbing solution in a strippingzone; (e) removing an aqueous stream containing flyslag particles fromsaid stripping zone, and passing said aqueous stream to a concentratingzone; (f) removing from said concentrating zone a concentrated aqueousstream derived from said aqueous stream and having a ratio of flyslagparticulate solids to liquid greater than that of the aqueous streamentering said concentrating zone; and (g) mixing a major portion of saidflyslag derived from at least one gasification reactor of step (a) and aminor portion of cementitious material and an effective amount of acomposition capable of converting sulfides in said flyslag at least tosulfur, with at least a portion of the concentrated stream from step(f), the concentrated aqueous stream being supplied in a ratio of fromabout one part to about five parts concentrated aqueous stream per part,by weight, combined total solids of flyslag and cementitious material,and producing a solid flyslag composite having improved disposalproperties.
 7. A process for removing flyslag from a synthesis gasstream from which the bulk of the flyslag has already been removedcomprising(a) passing said gas stream to a scrubbing zone, and scrubbingsaid gas stream with an effective amount of an aqueous scrubbing liquidcontaining ammonium polysulfide, and removing remaining flyslagparticles and HCN, NH₃, and COS from said gas stream, producing apartially purified gas stream substantially free of flyslag and a loadedaqueous scrubbing solution containing ammonium thiocyanate; (b)hydrolyzing the ammonium thiocyanate in at least a portion of saidloaded scrubbing solution, forming a hydrolyzed solution; (c) strippingH₂ S, NH₃, and CO₂ from at least a portion of said hydrolyzed solutionin a stripping zone; (d) removing an aqueous stream of stripped solutioncontaining flyslag particles from said stripping zone, and passing saidaqueous stream to a concentrating zone; (e) removing from saidconcentrating zone a concentrated aqueous stream derived from saidaqueous stream and having a ratio of flyslag particulate solids toliquid greater than that of the aqueous stream entering saidconcentrating zone; (f) mixing a major portion of flyslag havingsulfides present therein, a minor portion of cementitious material andan effective amount of a composition capable of converting sulfides insaid flyslag at least to sulfur, with at least a portion of theconcentrated aqueous stream from step (e), the concentrated aqueousstream being supplied in a ratio of from about one part to about fiveparts concentrated aqueous stream per part, by weight, combined totalsolids of flyslag and cementitious material, and producing a solidflyslag composite having improved disposal properties.
 8. A process forthe removal of flyslag from a gas stream containing flyslag, the flyslaghaving sulfides present therein and the gas stream derived from thegasification of coal, comprising(a) passing said gas stream containingsaid flyslag to a solids separation zone, and separating the bulk of theflyslag in said zone, producing solid flyslag and a gas stream havingreduced flyslag content; (b) passing gas stream having reduced flyslagcontent from step (a) to a scrubbing zone, and scrubbing said gas streamwith an effective amount of an aqueous scrubbing liquid containingammonium polysulfide, and removing HCN, NH₃, and COS and remainingflyslag particles from said gas stream, producing a partially purifiedgas stream substantially free of flyslag and a loaded aqueous scrubbingsolution containing ammonium thiocyanate; (c) hydrolyzing the ammoniumthiocyanate in at least a portion of said loaded scrubbing solution,forming a hydrolyzed solution; (d) stripping H₂ S, NH₃, and CO₂ from atleast a portion of said hydrolyzed solution in a stripping zone; (e)removing an aqueous stream of stripped solution containing flyslagparticles from said stripping zone, and passing said aqueous stream to aconcentrating zone; (f) removing from said concentrating zone aconcentrated aqueous stream derived from said aqueous stream and havinga ratio of flyslag particulate solids to liquid greater than that of theaqueous stream entering said concentrating zone; and (g) mixing a majorportion of flyslag from step (a), and a minor portion of cementitiousmaterial and an effective amount of a composition capable of convertingsulfides in said flyslag at least to sulfur, with at least a portion ofthe concentrated stream from step (f), the concentrated aqueous streambeing supplied in a ratio of from about one part to about five partsconcentrated aqueous stream per part combined total solids of flyslagand cementitious material, and producing a solid flyslag compositehaving improved disposal properties.
 9. A process for the gasificationof coal comprising(a) partially combusting particulate coal in agasification zone comprising at least one gasification, reactor, andproducing a hot gaseous stream containing synthesis gas, flyslag havingsulfides present therein and minor amounts of HCN, NH₃, and COS; (b)cooling said gaseous stream, and removing at least the bulk of theflyslag therefrom, producing a cooled gaseous stream having reducedflyslag content; (c) passing cool gas stream having reduced flyslagcontent from step (b) to a scrubbing zone, and scrubbing said gaseousstream with an effective amount of an aqueous scrubbing liquidcontaining ammonium polysulfide, and removing HCN, NH₃ and COS andremaining flyslag particles from said gas stream, producing a partiallypurified gas stream substantially free of flyslag and a loaded aqueousscrubbing solution containing ammonium thiocyanate; (d) hydrolyzing theammonium thiocyanate in at least a portion of said loaded scrubbingsolution, forming a hydrolyzed solution; (e) stripping H₂ S, NH₃ and CO₂from at least a portion of said hydrolyzed solution in a stripping zone;(f) removing an aqueous stream of stripped solution containing flyslagparticles from said stripping zone, and passing said aqueous stream to aconcentrating zone; (g) removing from said concentrating zone aconcentrated aqueous stream derived from said aqueous stream and havinga ratio of flyslag particulate solids to liquid greater than that of theaqueous stream entering said concentrating zone; and (h) mixing a majorportion of flyslag derived from at least one gasification reactor ofstep (a), a minor portion of cementitious material, and an effectiveamount of a composition capable of converting sulfides in said flyslagat least to sulfur, with at least a portion of the concentrated streamfrom step (g), the concentrated aqueous stream being supplied in a ratioof from about one part to about five parts concentrated aqueous streamper part, by weight, combined total solids of flyslag and cementitiousmaterial, and producing a solid flyslag composite having improveddisposal properties.